The disclosure relates to a hydraulic valve arrangement, in particular for pressure and/or volume flow control of a hydraulic machine, in particular a hydraulic pump, and to a hydraulic machine arrangement having a valve arrangement of this kind.
A hydraulic valve arrangement of this kind is known from Datasheet RD 92703/08.11 of the applicant and is used, in particular, in pressure and delivery flow control of hydraulic pumps, in particular axial piston pumps. The valve arrangement has a first valve, or a delivery flow control valve, by means of which the delivery volume flow of the hydraulic pump can be controlled. Control is effected by supplying a working space of an adjusting device of the hydraulic pump with an adjusting pressure controlled by the delivery flow control valve, leading to adjustment of a geometric swept or delivery volume of the hydraulic pump. For this purpose, a valve body of the delivery flow control valve is acted upon in the direction of a reduction of the geometric delivery volume, or in the direction of pressurization of the working space, by the pump pressure and in the direction of an increase in the geometric delivery volume, or of pressure relief of the working space, by a control pressure acting in the opposite direction and by a pressure equivalent of a control spring of the delivery flow control valve.
In this case, the control pressure used for this purpose is diverted from the high pressure or pump output pressure via a restriction device. For this purpose, the valve arrangement has a pressure medium passage which passes through the valve body of the delivery flow control valve and has a tapering segment, in particular a nozzle segment, with a minimum cross section. The pressure medium passage passes through the valve body from a pressure space that can be supplied with the high pressure toward a rear control space, in which the control pressure is effective. The control pressure is established downstream of the minimum cross section.
In this solution, limitation of the pump output pressure is accomplished by virtue of the fact that the control pressure produced in this way and acting on the valve plunger of the delivery flow control valve is limited by means of a second valve, or pressure limiting valve, of the valve arrangement. In this case, a valve plunger of the pressure limiting valve is acted upon in the direction of a connection of the control pressure to a pressure medium sink by the control pressure and by a pressure equivalent of an electromagnet and is acted upon in the closing direction of said connection by the pressure equivalent of an adjustable control spring. Accordingly, the set limit of the control pressure is smaller, the larger the actuating force of the electromagnet of the limiting valve. Since the pump pressure is controlled in such a way by means of the delivery flow control valve that it is higher by the pressure equivalent of the control spring than the control pressure, the pressure limiting valve and the set limiting value of the control pressure can be used to limit the high pressure or pump output pressure supplied by the hydraulic pump.
The disadvantage of this solution is that the pressure medium passage passing through the valve body of the delivery flow control valve is susceptible to soiling or blockage by dirt particles entrained in the pressure medium. The narrowing of the cross section resulting from such soiling leads to an increase in the pressure drop and hence to a distorted or lower control pressure. As a result, the pump output pressure formed is lower than that specified. Moreover, the soiling of the pressure medium passage can lead to instability in the control of the pump output pressure. In order to remove the soiling, normal operation has to be interrupted and the soiling has to be removed by expensive maintenance measures.
DE 199 53 170 A1 also shows a hydraulic valve arrangement of this kind having a delivery flow control valve and furthermore having a control valve which limits a delivery rate of the hydraulic pump in interaction with a power control valve coupled to an adjusting device of the hydraulic pump and designed as a pressure limiting valve. In this valve arrangement, the valve plunger of the control valve is penetrated from a pressure space subjected to the pump output pressure toward a rear space, in which the control pressure is effective, by a pressure medium passage having a constriction which is arranged at the end of the pressure medium passage and by means of which the pump pressure is throttled to the control pressure. In this solution too, the pressure medium passage is susceptible to soiling by metal fragments in the pressure medium or other dirt particles, as a result of which the control pressure can be distorted as in the solution described above. Since the valve plunger of the control valve is acted upon by the control pressure, the distortion thereof leads to distortion of the power control of the hydraulic pump.
Thus, both solutions have the disadvantage that the risk of control pressure distortion is high since the pressure medium passage can easily become clogged by dirt particles entrained in the pressure medium volume flow. In addition, there is the fact that removal of the soiling from the pressure medium passage involves a great deal of effort in terms of maintenance and entails interrupting normal operation of the valve arrangement.
Given this situation, it is the underlying object of the disclosure to provide a hydraulic valve arrangement which involves a reduced outlay in terms of maintenance. It is furthermore the underlying object of the disclosure to provide a hydraulic machine arrangement having a valve arrangement of this kind.